Stationary guide vanes and rotating turbine blades in gas turbines often have internal cooling channels. Cooling effectiveness is important in order to minimize thermal stress on these airfoils. Cooling efficiency is important in order to minimize the volume of air diverted from the compressor for cooling.
Film cooling provides a film of cooling air on outer surfaces of an airfoil via holes in the airfoil surface from internal cooling channels. Film cooling can be inefficient, because so many holes are needed that a high volume of cooling air is required. Thus, film cooling has been used selectively in combination with other techniques.
Impingement cooling is a technique in which perforated cooling tubes are inserted into span-wise channels in an airfoil to create impingement jets against the inner surfaces of the airfoil. A disadvantage is that warmer post-impingement air moves along the inner surfaces of the airfoil and interferes with the impingement jets. Impingement tubes require a nearly straight airfoil for insertion, but some turbine airfoils have a curved span for aerodynamic efficiency.
Another technique uses serpentine cooling channels that go from one end of the airfoil to the other and back. Air in such channels is much cooler at the beginning of the flow sequence, so it can cool the airfoil unevenly.
The present invention provides high efficiency, a cooling rate topography that matches the heating topography of an airfoil, coolant revival at mid-flow, and reduction of differential thermal expansion. It does not require impingement tube inserts, and can be formed in curved airfoils. Thus, it overcomes all of the above-mentioned disadvantages.